Heretofore the prior art has proposed various pressure control devices for use in a control system of an automatic transmission of an automotive vehicle. Such control devices are to a great extent operating within an area of the transmission which is filled with a fluid medium. Also such control devices, especially because of their dimensional tolerances, are susceptible to becoming operationally fouled as by foreign matter carried by the fluid medium the pressure of which is being controlled or regulated by the pressure control device. Also, it has been discovered that gases, such as air, entrained in the fluid medium also form as pockets within the pressure control device and inhibit proper functioning of such pressure control device.
It has been proposed that a calibrated restricted flow passage be formed within the pressure control device whereby a small portion of the fluid medium being regulated is flowed into and through the electrical motor means of the pressure control device to thereby, in effect, wash foreign matter as into sump while permitting the fluid medium, as flows into the area of the electrical motor means, to purge air from such pressure control device The provision of such a calibrated restricted flow passage has, for the most part, greatly enhanced continued proper operation of such pressure control devices. The problems associated with a calibrated restricted flow passage include the relative difficulty of forming a passage having a diameter in the order of 0.006 to 0.008 inch. In some operating environments it was found that the particle size of the entrained or carried foreign matter was such as to actually flow through the calibrated restricted flow passage and into the area of the electrical motor means thereby presenting the opportunity for foreign particle fouling of the electrical motor means. In some situations it was found that foreign particles could become lodged within the calibrated restricted flow passage thereby reducing the flow of fluid medium therethrough to a rate less than desired. The forming of the calibrated restricted flow passage to be of even smaller diameter did not present a believed acceptable solution in that the resulting flow therethrough was less than desired and the possibility of having foreign particles become lodged therein still existed.
The invention as herein disclosed and described is primarily directed to the solution of the foregoing as well as other related and attendant problems of the prior art.